1. Field of the Invention
The present invention relates to a high pressure seal which is subjected to substantial variations in fluid pressure against the high pressure side of the seal, and more particularly to such a seal which is adapted for use in a high pressure fluid pump.
2. Background Art
There are various applications for high pressure pumps, one being to supply very high pressure fluid, (e.g. water at a pressure of 10,000 psi to 100,000 psi or possibly more) so that this water may be discharged in the form of a high velocity water jet which can be used for cutting, abrading, etc. A common configuration for such a pump is to employ a piston which reciprocates in a high pressure cylinder to direct the fluid (generally water) to a manifold from which the water is guided (plumbed) to a nozzle and then discharged as the high pressure jet. On the pressure stroke, the plunger or piston can generate pressures in excess of 25,000 psi, while during the intake stroke the pressure in the cylinder chamber is substantially zero or very low.
There are a number of critical problems associated in the design and operation of such a high pressure fluid pump assembly. One of these problems is providing adequate seals, particularly in those areas where the seal is exposed to greatly fluctuating pressures. To provide an effective seal assembly in this environment, generally several seal components are used in combination. It is quite common to use an elastomeric ring member (commonly called an O-ring) as part of such seal assemblies. Quite often such O-rings are placed in a groove of another member so as to be exposed to the high fluid pressures, with the O-ring deforming under the high pressures to cooperate in providing the overall seal. However, it has been found that even in those areas where there is a so-called "static seal," quite often these O-rings are subject to early deterioration, this resulting in frequent shutdown of the equipment for repair or replacement of the seal assembly or its components.
A search of the prior art has disclosed a number of patents, these being the following:
U.S. Pat. No. 2,914,368 (Farmer, et al) relates to a seal for a piston-cylinder fluid motor. Two O-rings are mounted at opposite ends of the piston, and this system is such that fluid can be introduced under pressure on either side of the piston to move the piston toward one side or the other. There are two O-rings 46 and 47, and these are positioned in circumferential grooves at the axial ends of the piston, so as to form sliding seals with the inner surface of the cylinder. There are two passageways 48 and 49 which lead from the respective chambers of the cylinder (on opposite sides of the piston) and into a radially inward bottom wall of a groove for the related O-ring 46 or 47. The problem toward which this patent is directed is to alleviate the tendency of the O-rings to roll during operation, and thus produce a pumping action during cycling of the motor, so that a buildup of pressure occurs in the area between the O-rings. With reference to FIG. 3 of that patent, it can be seen that there are two passageways 48 and 49 which lead from respective chambers in the cylinder (on opposite sides of the piston) and into a radially inward bottom wall for the grooves for the O-rings 46 and 37. The operation is such (see FIG. 3 of that patent) so that when the piston moves to the right the pressure enters the passageway 48 to help push the O-ring 46 against the backup ring 41 to form a seal. However, on the low pressure side of the piston, there occurs the problem of the rolling of the O-ring to cause fluid pressure between the O-rings 46 and 47. On the low pressure side, the passageway 49 acts as a pressure relief passageway to permit the escape of the fluid to alleviate this pressure buildup. Thus, the problem toward which this patent is directed is that of alleviating a pressure buildup due to the rolling action of the O-ring where the O-ring is in engagement with the moving surface of a dynamic seal, such as a cylinder surface with the O-ring being part of a reciprocating piston.
U.S. Pat. No. 3,685,840 (Henry) relates to a seal arrangement for a high pressure pump where there is a reciprocating piston. There are two sets of seal members 46-48 and 36-38. The patent is directed toward a means of inserting lubricating fluid from a passageway 24 into accurate grooves 62 and 68. On the pressure stroke, there is sufficient pressure in the recesses 52, 58 and 42 so as to press the lip 44 into sealing engagement against the surface 18 and also
pressure the lips 54 and 60 against one another, thus crating a seal. However, on the intake stroke, the pressure of the lubricating fluid in the passageway 24 is sufficient to cause these lips 54 and 60 to part, and also to cause the lip 44 to move away, thus permitting lubricating fluid to enter into the area of the seal 36-38 and 46-48.
U.S. Pat. No. 3,132,568 (Strader) shows a seal for a high pressure piston where there is a wiper ring 52 exposed to the pressurizing fluid, the purpose of this wiper ring 52 being to prevent foreign material from coming into the area of the seal element so as to cause wear of these. There are three seal rings, 61, 62 and 63, each having a "v" shaped cross-section. There is provided a passageway 65-55 which leads into a radial passageway 67, each passageway being formed in an adapter 43. These passageways provide direct fluid pressure against the packing ring 61-63 so as to improve their sealing capability. In addition, this provides fluid pressure on both sides of the wiper ring 52 which is alleged to improve the wiping action to prevent foreign matter from coming into contact with the packing rings 61-63, a screen 48 is provided at the entrance of the passageway 66.
U.S. Pat. No. 4,478,423 (Hjelsand, et al) shows a high pressure seal for use in conjunction with a reciprocating plunger which is used to pump fluids such as cement slurries, fracturing slurries, acids and the like under pressure into an oil well. A prior art seal is shown in FIG. 1, and there is a brass header ring adapter 64 behind which is an elastomeric header ring 26 constructed of rubber having a hardness of 70 to 80 durometer, behind which are packing rings 42 and 44 that have in cross-section a "V" shape. There is a female adapter ring 50 made of brass and a "V" shaped anti-extrusion adapter ring 52 disposed between the last "V" shaped packing ring and the female adapter 50. The improvement which is the substance of this patent is shown in FIG. 2, and this comprises a wiper seal 100 having a "T" shaped in cross-section and having openings around the periphery of this seal ring. This permits a passage of a certain amount of fluid between the piston and this seal 100 because the seal 100 deforms into the apertures 216. This occurs in the event that some of the liquid being pumped escapes past the main seal made up of the components 26, 42, 44, 52 and 60.
U.S. Pat. No. 2,723,268 (Duval) shows a seal arrangement, for an hydraulic piston where there is a triangularly shaped seal (i.e. a cross-sectional triangular shape) where the apex of the triangle bears against the piston wall. There is a passageway connecting to the radially inward surface of the seal ring, and this is directed toward the high pressure side of the piston. This causes pressurization of the radially inward wall of the ring to press it outwardly against the cylinder, thus creating a better seal. An opposite arrangement is shown in FIG. 2 of that patent.
U.S. Pat. No. 1,618,611 (Burstall) shows a seal arrangement for a reciprocating piston where in one configuration the seal has a radially inward face which is exposed to high pressure by means of a passageway. This causes the seal ring to expand outwardly to engage the cylinder wall more closely and thus provide a more effective seal. It appears that this can also be done in a reverse manner so that the pressure is applied on the outside of the seal ring to cause it to squeeze inwardly against the cylinder member which then moves relative to the seal.